Method for determining the fuel content of the regeneration gas in an internal combustion engine comprising direct fuel-injection with shift operation

ABSTRACT

A method for determining the fuel content of a regeneration gas during regeneration of an intermediate fuel vapor storage unit in internal combustion engines with gasoline direct injection in lean (stratified) mode. Stored fuel vapor is supplied to the engine as regeneration gas via a controllable tank venting valve. The signal of an exhaust gas analyzer probe in the exhaust gas is considered for determining the fuel content of the regeneration gas. An adjustment between the analyzer probe signal and a preselected setpoint occurs while the tank venting valve is closed. The analyzer probe signal is combined with a correction quantity while the tank venting valve is closed, so that the combination corresponds to the setpoint. The analyzer probe signal is combined in the same manner with the previously obtained correction valve while the tank venting value is open. Regeneration gas charge is determined from this combination.

FIELD OF THE INVENTION

The present invention relates to the technical background of tankventing in internal combustion engines with gasoline direct injection.

BACKGROUND INFORMATION

Engines having gasoline direct injection may be operated in bothstratified mode and homogeneous mode.

An engine control program that controls switching between the two modesof operation is described in German Published Patent Application No. 19850 586.

In stratified mode, the engine is operated with a highly stratifiedcylinder charge and a very lean mixture to minimize fuel consumption.The stratified charge is achieved by late fuel injection, which dividesthe combustion chamber into two zones: The first zone contains acombustible air/fuel mixture cloud near the spark plug. It is surroundedby the second zone, which includes an insulating layer of air andresidual gas. The potential for optimizing consumption derives from theability to operate the engine largely unthrottled, thus avoiding chargecycle losses. Stratified operation may be performed when loads arecomparatively low.

At higher loads, when performance optimization is important, the engineis operated using a homogeneous cylinder charge. This homogeneouscylinder charge results from early fuel injection during intake. Thisresults in a longer interval between combustion and mixture formation.The potential of this mode to optimize performance derives, for example,from its ability to utilize the entire combustion chamber volume forfilling with combustible mixture.

Varying amounts of fuel vapor per time unit exist in the fuel tank of avehicle, depending on fuel temperature, fuel type and pressure ratios. Amethod is conventional known for first storing this fuel vapor in anactive charcoal filter and then supplying it, mixed with air, to theengine combustion system via a controllable tank venting valve duringoperation of the internal combustion engine. The active charcoal filterthus becomes able again to absorb additional fuel vapor (regeneration).The fuel vapor that has been mixed with air is referred to asregeneration gas.

To compensate for the amount of fuel flowing via the tank venting valve,the amount of fuel flowing via the injectors is reduced. In thisconnection, a method for obtaining a measure FTEAD of the fuel contentof the regeneration gas from known quantities in the control unit,including the fuel flow via the injectors, the quantity of regenerationgas when the tank venting valve is open, the intake air quantity of theengine and the signal of an exhaust gas analyzer probe, is described inGerman Published Patent Application No. 38 13 220 for engines withintake-manifold injection. The obtained measure serves to adjust thereduction in fuel flow via the injectors with the fuel flow via the tankventing valve, with the goal of controlling the composition of theentire air/fuel mixture. During operation of an engine withintake-manifold injection, the combustion chamber is homogeneouslyfilled with mixture, just like during operation of an engine withgasoline direct injection in homogeneous mode. It is therefore possibleto use tank venting control in this mode, as is conventional from thefield of intake-manifold injection.

During operation of an engine with gasoline direct injection instratified mode, on the other hand, disturbances tend to occur whencontrolling the entire air/fuel mixture with an open tank venting valve.

It is an object of the present invention to eliminate such disturbancesand thus improve predictability of the effect of tank venting on themixture composition in stratified mode.

SUMMARY

Specifically, the determination according to the present invention ofthe fuel content of a regeneration gas during regeneration of anintermediate fuel vapor storage unit in internal combustion engineshaving gasoline direct injection in lean (stratified) mode, in which thestored fuel vapor is supplied to the internal combustion engine in theform of regeneration gas via a controllable tank venting valve, and inwhich the signal of an exhaust gas analyzer probe in the exhaust gas ofthe internal combustion engine is taken into account to determine thefuel content, includes the following steps:

Adjustment between the exhaust gas analyzer probe signal and apreselected setpoint when the tank venting valve is closed, with theexhaust gas analyzer probe signal being combined with a correctionquantity when the tank venting valve is closed so that the result of thecombination corresponds to the setpoint.

Combination of the exhaust gas analyzer probe signal in the same mannerwith the correction value obtained earlier while the tank venting valveis open; and

Determination of the regeneration gas charge based on the result of thecombination.

The present invention is based on the concept that, in stratified mode,the measured lambda value may vary to a comparatively large degree fromthe physical lambda value.

Possible causes include probe manufacturing tolerances, aging effectsand greatly fluctuating exhaust gas temperatures in stratified mode withunregulated probe heating. Regardless of the cause at hand, a deviationnevertheless occurs between the probe signal and the actual lambdavalue.

It is an object of the present invention to adjust the probe signal instratified mode with the tank venting valve closed. This decouples theprobe signal from the absolute lambda value. If the regeneration gasadditionally has an effect when the tank venting valve is open, thiseffect may be determined from the relative change in the probe signal.

According to one example embodiment of the present invention, a measuredlambda value (measured lambda) is formed from the exhaust gas analyzerprobe signal, and the difference of the measured lambda value isdetermined from the product of the adjustment factor and the differenceof the lambda setpoint (setpoint lambda) from value 1 and integrated.

According to another example embodiment, the adjustment factor in thesteady state corresponds to the average quotient

(measured lambda−1)/(setpoint lambda−1).

With this function, fluctuations in the measured lambda are averaged outthrough the integration process during adjustment, thus preventingcorruption of the adjustment factor.

According to a further example embodiment, the actual lambda isdetermined by the following equation during operation with an open tankventing valve:

Actual lambda=(1/adjustment factor)*(measured lambda−1)+1

According to a further example embodiment, a new adjustment is performedin stratified mode upon a change in the operating point of the internalcombustion engine or when certain ambient conditions change.

According to a further example embodiment, the ambient temperature andthe altitude at which the engine is operated are ambient conditions ofthis type.

According to a further example embodiment, a change in the operatingpoint is defined by a minimum change in the lambda setpoint.

According to a further example embodiment, an adjustment ends when theabsolute value of the integrator input drops below a predeterminedthreshold value.

The present invention also relates to an electronic control unit forperforming at least one of the methods and example embodiments describedabove.

One example embodiment of the present invention is explained below onthe basis of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the technical background of the present invention.

FIG. 2 illustrates an example embodiment of the present invention in theform of function blocks.

DETAILED DESCRIPTION

Reference number 1 in FIG. 1 represents the combustion chamber of acylinder of an internal combustion engine. The inflow of air into thecombustion chamber is controlled by an intake valve 2. The air is drawnin via an intake manifold 3. The intake air volume may be varied by athrottle valve 4, which is controlled by a control unit 5. Signalscorresponding to a torque request by the driver, for example, theposition of a gas pedal 6, a signal corresponding to engine speed n ofan engine speed sensor 7, and a signal indicating the volume ml ofintake air from an air-flow sensor 8 are supplied to the control unit,and a signal Us indicating the exhaust gas composition and/or exhaustgas temperature is supplied by an exhaust gas sensor 16. Exhaust gassensor 16 may be, for example, a lambda probe, whose Nernst voltage orpump current (depending on the probe type) specifies the exhaust gasoxygen content. The exhaust gas is conducted through at least onecatalytic converter 15, which converts pollutants from the exhaust gasand/or stores them temporarily.

Control unit 5 forms output signals from these and possibly other inputsignals corresponding to other internal combustion engine parameters,such as intake air and coolant temperature, for the purpose of settingthrottle valve angle alpha by an actuator 9 and for the purpose ofcontrolling a fuel injector 10, thereby metering the fuel to the enginecombustion chamber. The control unit also controls ignition triggeringvia ignition unit 11.

Throttle valve angle alpha and injection pulse width ti may be importantmanipulated variables to be tuned to each other for achieving thedesired torque. A further important manipulated variable for influencingtorque may be the angular ignition angle relative to piston movement.The determination of the manipulated variables for setting torque is thesubject matter of German Published Patent Application No. 198 51 990,which is expressly incorporated herein in its entirety by referencethereto.

The control unit also controls a tank venting system 12 as well as otherfunctions for achieving efficient combustion of the air/fuel mixture inthe combustion chamber. The gas force resulting from combustion isconverted to a torque by piston 13 and crank mechanism 14.

Tank venting system 12 includes an active charcoal filter 15, whichcommunicates via corresponding lines or connections with the tank,ambient air and intake manifold of the internal combustion engine, witha tank venting valve 16 being provided in the line to the intakemanifold.

Active charcoal filter 15 stores fuel vaporizing in tank 5. As tankventing valve 11 is opened by control unit 6, air is drawn in fromenvironment 17 through the active charcoal filter, which releases thestored fuel into the air. This air/fuel mixture, which is also referredto as tank venting mixture or regeneration gas, affects the compositionof the entire mixture supplied to the internal combustion engine. Thefuel component of the mixture is further determined by metering fuel viafuel metering device 10, which is adjusted to the intake air rate. Inextreme cases, the fuel drawn in via the tank venting system may be in aproportion of approximately one third to one half of the total fuelvolume.

FIG. 2 is a function block diagram of the method according to thepresent invention.

The initial prerequisites are a closed tank venting valve and astationary operating state.

Block 2.1 provides the measured lambda value obtained from signal Us ofthe exhaust gas analyzer probe. Block 2.2 provides the setpoint forcomposition Lambda of the entire mixture combusted by the internalcombustion engine. Block 2.3 forms the difference between the setpointand value 1. This difference is combined with an adjustment factor inblock 2.4. Block 2.5 forms the difference between the measured lambdavalue and value 1. Block 2.6 determines the deviation between thedifference in the measured lambda value and the product of theadjustment factor and the difference between the lambda setpoint andvalue 1. This deviation is supplied to an integrator 2.7. Block 2.8supplies a correction value for operating points in the vicinity of theoperating point where the adjustment occurs. Assuming a steady operatingstate, as described above, block 2.8 supplies value 1, so that theoutput value of integrator 2.7 is not changed by the result of thecombinations in blocks 2.9 through 2.11.

In this case, the integrator output value is returned directly as theadjustment factor and combined with the desired lambda setpoint.

This structure has the following function:

As long as the product of the adjustment factor and the deviationbetween the desired lambda value and 1 is less than the deviationbetween the measured lambda value and 1, the integrator input ispositive, and the integrator output increases. The adjustment factor isthereby increased. This increases the product mentioned above. As aresult, the interval between the product and the deviation between themeasured lambda value and 1 decreases. The integrator input becomessmaller. The integrator output increases at a slower rate.

If the integrator output becomes too large, the feedback changes thesign of the integrator input, and the integrator output is subsequentlyreduced.

As a result, the adjustment factor in the transient state corresponds toa certain extent to the average quotient

(measured lambda−1)/(setpoint lambda−1).

With this function, fluctuations in the measured lambda may be averagedout through the integration process during adjustment, thus preventingcorruption of the adjustment factor.

During operation with an open tank venting valve, the actual lambda maybe determined by the following equation:

Actual lambda=(1/adjustment factor)*(measured lambda−1)+1

The actual lambda is proportionate to the quotient of the entire airvolume and entire fuel volume.

The entire air volume includes the air volume flowing via the throttlevalve and the air component of the regeneration gas from the tankventing system. The air component of the regeneration gas is more orless equivalent to the regeneration gas volume. The latter may bederived from known quantities in the control unit, such as intakemanifold pressure and control pulse-duty factor. The air component istherefore known. The same is true for the air volume flowing via thethrottle valve, which is detectable, for example, by a hot-film air massmeter. The fuel volume flowing via the injectors may be derived from thecontrol pulse widths and the pressure in the fuel system, i.e., fromknown quantities.

The fuel component of tank venting in the method according to thepresent invention may therefore also be determined in stratified modefrom the measured lambda value using the adjustment factor.

Blocks 2.12 through 2.17 represent a structure for activating theadjustment. A new adjustment in stratified mode occurs upon a change inthe operating point of the internal combustion engine or upon a changein certain ambient conditions. Examples of such ambient conditions areambient temperature, which may be provided, for example, by an intakeair temperature sensor, and the altitude at which the engine isoperated. Information about this altitude is available in modern enginecontrollers. It is determined, for example, from the signal of anambient pressure sensor or calculated from the detected load (intake airvolume, cylinder charge). A change in the operating point is alsodefinable, for example, as a minimum change in the lambda setpoint, forexample by a minimum value of 0.3. If one of these conditions occurs,block 2.12 causes the tank venting valve to close in block 2.14 viaflip-flop 2.13 and starts integrator 2.7.

Blocks 2.15 through 2.17 detect the end of the adjustment. Block 2.15provides a threshold value DLAMSCE, and block 2.16 supplies the positiveabsolute value of the integrator input. If this value drops below thespecified-threshold value, block 2.17 detects this condition and cancelsthe command to close the tank venting valve by resetting flip-flop 2.13.

Blocks 2.8 through 2.11 make it possible to take into account minorchanges in the lambda setpoint that do not represent a change in theoperating point in the above sense.

The relationship between the probe voltage and the lambda value isgenerally nonlinear.

A new adjustment thus occurs in the event of major changes in the lambdasetpoint (change in operating point). In the event of minor lambdasetpoint changes, block 2.7 supplies a correction quantity instead, forexample on the basis of a computerized linearization of the relationshipbetween Us and lambda setpoint an environment of the adjusted operatingpoint.

What is claimed is:
 1. A method for determining a fuel content of aregeneration gas upon regeneration of an intermediate fuel vapor storageunit in an internal combustion engine, comprising: performing gasolinedirect injection in lean mode; supplying stored fuel vapor to theinternal combustion engine in the form of the regeneration gas via acontrollable tank venting valve; determining the fuel content of theregeneration gas in accordance with a signal of an exhaust gas analyzerprobe in an exhaust gas of the internal combustion engine; performing,with a closed tank venting valve, an adjustment between the signal ofthe exhaust gas analyzer probe and a preselected setpoint in which theexhaust gas analyzer probe signal is combined with a correction quantitywhile the tank venting valve is closed so that a result of thecombination corresponds to the setpoint; combining, with an open tankventing valve, the exhaust gas analyzer probe signal with the correctionquantity; and determining a regeneration gas charge from the result ofthe combination.
 2. The method according to claim 1, further comprisingthe steps of: forming a measured lambda value from the exhaust gasanalyzer probe signal; and determining and integrating a difference ofthe measured lambda value from a product of an adjustment factor and adifference of a lambda setpoint from value
 1. 3. The method according toclaim 2, wherein the adjustment factor in a steady state corresponds toan average quotient in accordance with: (measured lambdavalue−1)/(lambda setpoint value−1).
 4. The method according to claim 2,further comprising the step of determining an actual lambda inaccordance with the following equation during operation with the opentank venting valve: actual lambda=(1/adjustment factor)*(measured lambdavalue−1)+1.
 5. The method according to claim 1, farther comprising thestep of performing an adjustment in stratified mode upon one of a changein an operating point of the internal combustion engine and a change inambient conditions.
 6. The method according to claim 5, wherein theambient conditions include an ambient temperature and an elevation atwhich the internal combustion engine is operated.
 7. The methodaccording to claim 5, wherein the change in the operating point includesa minimum change in a lambda setpoint.
 8. The method according to claim2, further comprising the step of completing an adjustment when anabsolute value of an integrator input drops below a preselectedthreshold value.
 9. An electronic control system configured to perform amethod for determining a fuel content of a regeneration gas uponregeneration of an intermediate fuel vapor storage unit in an internalcombustion engine, the method including the steps of: performinggasoline direct injection in lean mode; supplying stored fuel vapor tothe internal combustion engine in the form of the regeneration gas via acontrollable tank venting valve; determining the fuel content of theregeneration gas in accordance with a signal of an exhaust gas analyzerprobe in an exhaust gas of the internal combustion engine; performing,with a closed tank venting valve, an adjustment between the signal ofthe exhaust gas analyzer probe and a preselected setpoint in which theexhaust gas analyzer probe signal is combined with a correction quantitywhile the tank venting valve is closed so that a result of thecombination corresponds to the setpoint; combining, with an open tankventing valve, the exhaust gas analyzer probe signal with the correctionquantity; and determining a regeneration gas charge from the result ofthe combination.
 10. The electronic control system according to claim 9,wherein the method further includes the steps of: forming a measuredlambda value from the exhaust gas analyzer probe signal; and determiningand integrating a difference of the measured lambda value from a productof an adjustment factor and a difference of a lambda setpoint fromvalue
 1. 11. The electronic control system according to claim 10,wherein the adjustment factor in a steady state corresponds to anaverage quotient in accordance with: (measured lambda value−1)/(lambdasetpoint value−1).
 12. The electronic control system according to claim10, wherein the method further includes the step of determining anactual lambda in accordance with the following equation during operationwith the open tank venting valve: actual lambda=(1/adjustmentfactor)*(measured lambda value−1)+1.
 13. The electronic control systemaccording to claim 9, wherein the method further includes the step ofperforming an adjustment in stratified mode upon one of a change in anoperating point of the internal combustion engine and a change inambient conditions.
 14. The electronic control system according to claim13, wherein the ambient conditions include an ambient temperature and anelevation at which the internal combustion engine is operated.
 15. Theelectronic control system according to claim 13, wherein the change inthe operating point includes a minimum change in a lambda setpoint. 16.The electronic control system according to claim 10, wherein the methodfurther includes the step of completing an adjustment when an absolutevalue of an integrator input drops below a preselected threshold value.